1. Field of the Invention
The invention relates to posture chairs having a seat and a back provided with means for adjusting the height of the back and for permitting it to rock back and forth against spring-bias.
2. Prior Art
Various posture chairs as just described are known in the art. See, for example, U.S. Pat. Nos. 2,018,825; 2,158,453; 2,257,583; 2,328,243; 2,329,673; and, 2,570,177. All of these show the back mounted for rocking back and forth against the compression springs enclosed in a tube or pipe. These prior art devices suffer the disadvantages, however, that, the spring pipes are either mounted alongside the seat and thus exposed, or require a specially modified seat to accomodate the pipe springs; that, the spring pipes are individually attached to separate back support members located at the sides of the back portion, with the result that when a greater load is applied to one side of the back portion, correspondingly greater tension will be placed on the spring on that side of the chair; that, the pipe springs are attached by a single projecting bolt or lug which is placed under torque and in single shear when the spring pipe is loaded; that, adjustment of the height of the back involves multiple adjustment, an adjustment for each of the side supports or an adjustment at each end of the spring pipe; that, in all of the prior art devices except those of the said U.S. Patents, the force with which the back pushes back increases the farther it is pushed back, whereas in the devices of the cited U.S. Patents, the opposite is the case, namely, the force decreases, but in that case it decreases to such an extent that it is frequently difficult for a person to right himself without undue strain on his abdominal muscles; that, simultaneous single-control adjustment of the height of the back and the depth of the seat, where possible, does not provide adequate seat-depth adjustment.